1. Field of the Invention
This invention relates to reactor cores, for example cores for reactors used with rotating dynamoelectric machines, and more particularly to core clamping and air gap arrangements for such reactor cores.
2. Description of the Prior Art
The prior art discloses many examples of reactor cores composed of a plurality of laminations and in many cases having one or more air gaps arranged therein. Such reactor cores usually include a plurality of legs and the air gap or gaps are arranged in one or more of these legs. The gap is normally provided by spaced faces perpendicular to the leg in which the gap is located. The prior art also includes arrangements for adjusting the size of the gap to vary the reactance of the reactor of which the core is a part.
Such reactors may be used for example in connection with dynamoelectric machines. In this type of use such a reactor may be employed in series with each of the legs of a primary winding of an excitation transformer, the secondary of which may be in circuit with an SCR for controlling the field excitation of the dynamoelectric machine; for example, it may be used in a circuit such as that shown in U.S. Pat. No. 3,702,965, assigned to the assignee of the present invention.
Particularly in such uses involving relatively large currents the reactor core may have substantial magnetic flux therethrough and this flux tends to move the parts of the core on opposite sides of an adjustable air gap toward each other with substantial force. In order to counteract the effect of this force and maintain the desired air gap, some prior art structures have employed spacers of non-metallic material in the air gap which block the same.
However, such cores are also subject to development of substantial heat therein and it is necessary to circulate cooling gas through the core to effect removal of this excess heat. One convenient path for flow of such gas to remove excess heat is through the air gaps in the core but the inclusion of the aforementioned spacers blocks, or at least partially obstructs, the flow of gas, thereby reducing the cooling effectiveness. Additionally, such spacers cannot be relied upon, under heavy-duty conditions over a long period of time, as for example the uninterrupted operating cycle of an electric utility generator which may run for years without shutdown, to adequately perform the air gap maintenance function. In such installations with large air gaps intense heat is generated. Mechanical spacers are susceptible, under such conditions over such time periods, to deterioration and change of dimension. This can lead to clearances and loosening of the spacers, which in turn can lead to vibration of the magnetic parts, wear, and eventual failure of the reactor.
Moreover, the extent of cooling is also affected by the extent of the surface area of the opposed faces on opposite sides of the air gaps. In the usual prior art structure the gap has been formed so that these faces are perpendicular to the core leg and the surface area is therefore limited to the cross-sectional area of the leg. In accordance with the present invention the gap is formed to extend diagonally of the core leg thereby materially increasing the surface area of the faces on opposite sides of the gap and hence increasing the surface contacted by the cooling gas flowing through the gap to remove heat from the core.
The force tending to urge the parts of the reactor core on opposite sides of the gap toward each other is dependent upon the flux density at the gap. With prior art structures in which the gap is made so that the faces are perpendicular to the leg of the core there is a substantial flux density and hence a substantial force which has to be counteracted in order to maintain the gap at its desired size. With the diagonal air gap arrangement of the present invention the surface area at the gap is materially increased and the flux density across the gap for a given flux density in the reactor core is correspondingly reduced, thereby reducing the force which must be counteracted in maintaining the gap size.
In such reactor cores it is desirable to provide means for adjusting the size of the gap in order to vary the reactance of the reactor of which the core is a part. In accordance with the present invention the adjustment is conveniently made by simply loosening fastening means accessible from the exterior of the reactor core making the desired adjustment and then tightening the fastening means to hold the parts in the adjusted position. Moreover, the aforementioned diagonal gap provides "fine tuning" in facilitating accurate adjustment of the gap.
Accordingly, it is a principal object of the invention to provide laminated core structure for inductive devices which has greater support in opposition to magnetic forces than was heretofore available.
It is another object of the present invention to provide a reactor core having an improved arrangement for adjusting an air gap therein.
It is still another object of this invention to provide a reactor core which requires no spacers in the air gap thereby leaving an unobstructed passage for flow of cooling gas.
It is a further object of this invention to provide a reactor core having an air gap arranged in a manner which reduces flux density across the gap and thereby reduces the force tending to urge the faces of the core leg on opposite sides of the gap toward each other.
It is still a further object of this invention to provide an air gap arranged so as to maximize the cooling surface provided by the gap.
It is a further object of this invention to provide an adjustable air gap arranged so as to achieve "fine tuning" in the adjustment of the gap.
It is a further object of this invention to provide simple and effective means accessible from the exterior of the core for effecting adjustment of the air gap.